FIG. 1 is a schematic view of an armature prepared by the conventional process and FIG. 2 is a sectional view of an apparatus for the conventional method of connecting an armature coil of rotary machine.
Referring to FIGS. 1 and 2, the conventional method will be described. In FIGS. 1 and 2, (1) designates the shaft of a starter motor; (2) designates an armature core fixed to the shaft; (3) designates an armature coil held in a wound form in slots (not shown) provided in the armature core; (3a) designates a coil end of the armature coil; (4) designates a commutator to which the coil end (3a) of the armature coil is connected and which comprises a plurality of segments (5) positioned in a peripheral direction of the shaft (1) and a molded substrate (7) molded in one piece with a bushing (6) fitted on the shaft (1), the end portion of the segments (5) being bonded by the end portion (7a) of the molded substrate (7). The reference numeral (8) designates an ultrasonic welding apparatus for welding the segments (5) to the coil ends (3a) of the armature coil by ultrasonic wave; (9) designates a power source for producing ultrasonic wave; (10) designates a coil; (11) designates a magnetostriction transducing element; (12) designates a horn and (13) designates a tip.
A method of the ultrasonic welding of the segment (5) to the coil end (3a) of the armature coil (3) of the starter motor armature having the structure mentioned above will be described. The coil ends (3a) are superposed in parallel each other and laid on the segment (5) and the coil ends (3a) are pressed from the top by the tip (13) at a compressive force (Pa) and at the same time, ultrasonic vibration (Fa) is applied to the segment (5) secured in the axial direction of the shaft (1) in parallel to this direction as shown in FIG. 2. Frictional heat is produced in the coil end (3a) of the armature coil and the segment (5) by applying ultrasonic vibration energy to result in the welding of both members; thus, the armature coil is connected to the segment.
In the conventional ultrasonic welding method described above, it is necessary to prevent a peel-off phenomenon of the segment (5) from the molded substrate (7) and occurence of the cracking of the molded substrate end (7a), which cause overspeed strength failure of the commutator, because the ultrasonic vibration of the coil end (3a) caused by the friction excites the segment (5) to vibrate it. Accordingly, it is necessary to increase the bonded area between the segment and the molded substrate or to form the segment (5) in a complicated shape or to increase the thickness of the end portion (7a) of the molded substrate in order to enhance the bonding strength of the molded substrate (7) to the segment (5). These attempts result in the increase of production cost and poor mass productivity disadvantageously.